Could you tell me what are all of the leads to of depression ?

So many: Tough question. Some depressions are caused by hormonal or endocrine problems, some are inherited, some are due to old trauma, some are caused from substance abuse and some are situational. That's what psychiatrists are trained to sort out.

Leads of depression: Depression can related to neurotransmitter imbalances in the brain (serotonin, norepinephrine, or dopamine), hormone imbalances (estrogen, testosterone, cortisol, thyroid), genetic predisposition to mood disorders, head injuries, dealing with major stressors to include loss, alcohol or drug use and may occur as a side effect to some medications.